1. Summary of the Invention
This invention relates to a method and apparatus for testing gap filler materials and, more particularly, to a system for determining a plurality of mechanical and electrical properties of materials designed for use in filling spaces between aircraft plates.
2. Description of the Background Art
In the field of aircraft, metallic plates are coupled or otherwise secured together to lower base structures as by fasteners, set screws or other like mechanisms. Such other mechanisms are removable to allow for access to internal aircraft components and for the replacement and/or repair of the individual plates.
The proper engineering design of aircraft requires that adjacent plates be spaced a small distance from each other so as to allow for expansion and/or contraction of the plates during extreme thermal conditions. Such spacing also allows for plate shifting during the maneuvering of the aircraft during operation and use. Unfortunately, however, the spacing between plates creates a discontinuous surface which interrupts the laminar flow of air thereover. This results in undesirable drag, excessive sound, poor fuel consumption and diminished handling capabilities. In addition, the plates are normally electrically conductive thereby creating electrical discontinuities at the gaps which are detectable by radar. This is because the discontinuous electrical surfaces, as created by the spacings between plates, increases electrical interference when reflecting radar waves. This increases the detectability of the aircraft by radar.
From a commercial standpoint the most common technique for filling aircraft gaps is the use of an elastomeric filler material such as silicone, urethane or the like, foam or non-foamed, formed in place in the aircraft gap. Prior to forming, such filler material is loaded with an electrically conductive, electro-magnetic additive of a heavy metal such as nickel, silver, gold, ferraus metal or the like. Such filler material when properly loaded provides the desired electrical conductivity to abate electrical discontinuity. Unfortunately, however, determining the mechanical and electrical properties of such filler material, particularly while being subjected to varying mechanical and electrical conditions, is a difficult task.
The testing of mechanical and electrical properties of materials is the subject of a wide variety of commercial devices and patents. By way of example, note U.S. Pat. No. 4,095,461 to Starita. This patent measures shear properties of polymers while the present invention measures flatwise tensile strength, elongation, adhesion to substrates, fatigue capability and conductivity of conductive polymers, mechanical and electrical properties of the same time. U.S. Pat. No. 3,214,961 to Brown et al measures flatwise adhesion of sealant material between concrete members but not electrical properties, whereas the present invention tests conductive polymers and measures the flatwise tensile strength, elongation, fatigue capability and conductivity as well as the adhesion to a substrate. The same is true for U.S. Pat. No. 2,667,069 to Ramos et al. In addition, U.S. Pat. No. 4,089,211 to Vercellone et al; U.S. Pat. No. 2,595,069 to Fritz; U.S. Pat. No. 3,786,673 to Weissman and U.S. Pat. No. 3,621,711 to Griffith et al all relate to equipment for the testing of elastomeric materials, but none measures conductivity during flatwise tensile testing and fatigue cycles as in the present invention. Further, U.S. Pat. No. 3,572,102 to Baratta and U.S. Pat. No. 2,586,940 to Wolf are patents relating to electrical measurement. They have no relationship to the electrical measurements carried on during the flatwise tensile and fatigue testing as in the present invention. Lastly, U.S. Pat. No. 2,413,737 to Weaver relates to patch pull testing of aircraft skins and has no relationship to the flatwise tensile and fatigue testing of conductive polymers during electrical testing as in the present invention.
As illustrated by the large number of prior patents and commerical devices and techniques, efforts are continuously being expended in an effort to improve testing methods and apparatus for aircraft gap filler material and the like. Such efforts are being made to render the testing of such materials more efficient, reliable, inexpensive and convenient. None of these previous efforts, however, provides the benefits attendant with the present invention. Additionally, the prior patents and commercial devices and techniques do not suggest the present inventive combination of method steps and component elements arranged and configured as disclosed and claimed herein.
The present invention achieves its intended purposes objects and advantages through an unobvious combination of method steps and component elements, with the use of a minimum number of parts, at a reasonable cost to manufacture and use and by employing only readily available materials.
It is, therefore, an object of the present invention to provide an improved method and system for testing the mechanical and electrical properties of an electrically conductive specimen adapted for use in sealing gaps between aircraft panels, comprising a first device having a pair of electrically conductive interior plates positionable on opposite sides of a specimen, a pair of electrically insulating intermediate plates located on the sides of the interior plates remote from the specimen, a pair of electrically conductive exterior plates located on the sides of the intermediate plates remote from the specimen, means to couple to the exterior plates to drive means for imparting motion thereto with respect to the specimen, and means to couple the interior plates to electrical means for providing electrical current and for testing the electrical properties of the specimen during the operation of the drive means; and a second device having a pair of electrically insulating primary plates with interior portions spaced from each other, a pair of electrically conductive secondary plates secured to the interior portions of the primary plates so as to form a specimen-receiving space located entirely over only the interior portion of one of the primary plates, means to couple drive means with respect to the primary plates for imparting motion to at least one of the primary plates and its secured secondary plate with respect to the specimen, and attachment means to couple the secondary plates to electrical means for providing electrical current and for testing the electrical properties of the specimen during the operation of the drive means.
It is a further object of this invention to concurrently test aircraft gap filler material for mechanical and electrical properties.
It is a further object of the present invention to maximize specimen testing with minimum equipment.
It is a further object of this invention to manufacture superior aircraft.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.